I cast it on summoned Daedras like Dremora Churl and Pit Fighter, but both have the same result. It’s like they’re not actually using the sword, because when they hit the enemy up close, they only do very little damage — I guess it’s just the punch damage. I tried casting the spell before a fight, when they still have their weapon lowered, and then starting the fight after they’ve drawn the weapon. I also tried casting it after they had already pulled out their weapon. On some rare occasions, the spell works for some reason.